What you need is a gearing chart. I have one that includes compact gearing as well. PM me your fax number and I can send it to you.

no real difference between changing the cassette and changing the chainrings other than swapping the cassette out is cheaper.

---

---

"Here's how you run a marathon. Step 1: You start running. Step 2: There is no step 2." - Barney (How I Met Your Mother)

I don't believe you are correct. If you change the front chainrings (to compact rings) you will in turn change the gearing and rollout of all of the rear cassette rings. If you just change the cassette and not the front chainrings, then you only affect the gears you've either added or taken out on the new cassette.

do you mean, 50-34?
50-43 would be wierd (and harder low gears than a 53-39).
50-36 is also an option.
and there was a thread lately about putting 50-38 rings on a standard (i.e. non-compact) crank.

in order of price (cheapest to most expensive) i'm thinking it's new chainrings; new casette; new crankset.

My bad. Yes, I meant to say 50-34.

It would be prudent, I'm guessing, to change both the rear cassette, rear derailleur, and chain together. Therefore, cost would not be that much different from a new crank set. 'Course a compact crank might require a new front derailleur, too.

Any "fast riders" from IMWis want to voice what their easiest/hardest gears were for that race? I wouldn't think I really need the 39/25. There are lots of hills but none that are really bad. At the same time I do not recall even using the 53/11 except an occasional downhill.

I found the chart again on the net.
Here is the link:

http://www.fullspeedahead.com/...tio%20comparison.pdf

i know it sounds crazy (cause i thought it too) but go for a 11 or 12-27. I had 2 pros and 4 sub10 hour amatuers tell me this before last year's IMmoo. i thought a 27 sounded ludicrous considering I always fly past my group on hills and i had used a 9 speed 12-23 in lake placid the previous year (like you my cadence is around 100 for most races/rides and up hills).

Never know what kind of day your gonna have out there and having two extra large gears wont hurt you at all. I doubt anyone has been out on an IM racecourse thinking "gosh i wish i had two more small cogs to be able to go down and burn this thing up with" more than likley most of us have been out there wishing we had another gear to switch to to make some of the rollers ease our legs for the upcoming marathon.

think of it as risk vs reward. whats the risk of having a 25 or 27 cog out there? probbaly not much. but the reward is you have some extra possibilities to go in to if your legs start to go on the second loop (or it gets really windy). Just gives you some nice options to consider when your 80, 90 or100 miles into the race. I also liked having a 12-27 as it allowed me to be in the big ring up front and shift in to a 21,23, or 25 in the back when cresting over the small little rollers. Less shifting, and allowed me to keep more momentum going over those small hills. otherwise i might have had to either really kill myself in to hard a gear or to shift into the small chain and somewhere in the middle of the casette which takes away from my concentration and kills some of the momentum. take it for what its worth!

The first question is whether you use your 11 now. You say you have to stand for a lot of climbs so that suggests you need a smaller low gear. However, if you also use the 11, you don't want a compact. Your cheapest alternative is to put on an 11-25 or 11-26 (SRAM, assuming you use Shimano) if you do use the 11. You may also have to change your chain but don't need to do anything with the derailleur. If you don't use the 11, go for a 12-27 as has been suggested. If you're riding with 9 speed, cassettes aren't too expensive. If 10, they are. Do you have a friend or sympathetic LBS who could lend you a wheel with lower gearing?

voitgh,

Maybe I'm missing something but I think what you are looking for is a chart that indicates cadence for a particular gear combination and speed. I think Sheldon Brown's website can help you. At the very least I think he has the formula posted so that you could plug in your wheel size, speed and gear combination to get the cadence.

Then you can determine what cogs you want in your cassette.

Another great gearing resource is "Bicycle Gearing: a Practical Guide" by Rob Marr. That info is in there too.

---

Ben Cline


Better to aspire to Greatness and fail, than to not challenge one's self at all, and succeed.

I guess what I'm searching for is a "cheaper" way to figure out the best gearing for a race or training than to buy every bike part known to man--not to mention inventing some new ones along the way. Every bike store I've been to (15 in the past month) has the same answer to my questions about gearing; Just buy an 11-23 AND a 12-25 AND a 12-27 AND a compact crank AND...well, you get the point.

Back in the real world of limited income to spend that kind of money, I'm going to keep the 11-21 with the 53-39 crank and just f#$%ing deal with the hills when I get to them.

I do want to thank everyone for voicing their opinions and giving me some info to research.

boy that makes sense to me.....I don't know if that's a good thing or not.......

You don't need a new RD for the gearing choices you are contemplating.

You can make an Excel spreadsheet using these equations

Gear Inches = (Size of Chainring * Tire Diameter) / (Size of Cog in Rear Cassette)
Speed = (Gear Inches * Cadence) / 336.13544

These numbers are all ideal if you can maintain whatever cadence. Since it does not factor in weight, drag and all that other stuff I really would not pay attention to speed. If you know what power you can sustain, you can do a torque equation to figure out speeds, which would be a better method of calculating speed.

Tire (mm) 700
Tire (in.) 27.55905509
Cadence 100

Gear Inches Front Chainring
Front Chainring 53 42 50 34
Rear 11 133 105 125 85
Cogs 12 122 96 115 78
13 112 89 106 72
14 104 83 98 67
15 97 77 92 62
16 91 72 86 59
17 86 68 81 55
19 77 61 73 49
21 70 55 66 45
23 64 50 60 41

Speed
Front Chainring 53 42 50 34
Rear 11 39.6 31.2 37.2 25.3
Cogs 12 36.3 28.6 34.2 23.2
13 33.3 26.5 31.5 21.4
14 30.9 24.7 29.2 19.9
15 28.9 22.9 27.4 18.4
16 27.1 21.4 25.6 17.6
17 25.6 20.2 24.1 16.4
19 22.9 18.1 21.7 14.6
21 20.8 16.4 19.6 13.4
23 19 14.9 17.8 12.2